Field of Embodiments
The disclosed embodiments relate generally to an apparatus and methods for shredding recyclable material, such as paper.
Description of Related Art
Material containing information, especially recyclable material, is often shredded. The recyclable material may be shredded in any suitable environment. For example, the recyclable material may be shredded in a motor vehicle. A typical motor vehicle used to shred this recyclable material typically includes a compartment with a bin lifting device to load the recyclable material into the compartment, a shredder to shred the recyclable material in the compartment, a discharge conveying/packing element to pack the shredded recyclable material into a storage area within the compartment, an unloading device for unloading the shredded material from the storage area and a control system for controlling the motor vehicle. Other motor vehicles may additionally include a feeding element that includes a conveyor or a feed drum to control the input rate of the recyclable material into the compartment.
It can be desirable to shred recyclable material to a smaller size than a standard shred size, due to customer requirements and/or for commercial advantage, particularly, if it can be done at a less expensive price than competitors' prices. Additionally, the introduction of new security and privacy regulations and laws are changing the size to which the recyclable material is shredded. The demands of customers, the need to out price competitors and the introduction of the new security and privacy regulations and laws are becoming more prevalent.
Conventional shredders provide options for shredding the recyclable material to the size required for highly sensitive information. These options include two shaft shear shredders, strip shredders, single rotor shredders, hammermills and granulators.
Two shaft shear shredders include a first shear shredder and a second shear shredder. Two shaft shear shredders generally produce a width by length shred with the width generally controlled by the width of the knives on the shredders. Disadvantages result because it is difficult to control the length to which the recyclable material is shredded. An additional disadvantage is that the orientation of the recyclable material that enters the two shaft shear shredders can significantly impact the size of the shredded recyclable material. For example, when the recyclable material stands up vertically edgewise between knives on a shaft of a shredder, the interaction between the knives and the shaft causes the recyclable material to fold and pinch between the tip of the knives and a spacer, thereby resulting in the shredded recyclable material being able to unfold after shredding. Further disadvantages result because the amount of the recyclable material can adversely affect the size to which the recyclable material is shredded. For example, if a small amount of the recyclable material is loaded into the shredders, the recyclable material can be pulled through the shredders at knife tip speed to produce long strips or the recyclable material can get folded into the hooks of the knives, thereby preventing the recyclable material from being shredded to a desired shred size. Yet another disadvantage is that passing the recyclable material through a second shear shredder may not change the length of the recyclable material if the recyclable material passes through the shredder in a longitudinal direction. Moreover, another disadvantage results because the knives of the second shear shredder are more susceptible to damage when contaminants pass through the shredder than the knives of the first shear shredder due to the knives of the second shear shredder being smaller in width than the knives of the first shear shredder.
Strip shredders include two counter rotating shafts that pull the recyclable material into a nip point between two intermeshing cutting disks. The intermeshing cutting disks shear the recyclable material into strips. Shredding the recyclable material to the smaller size required for highly sensitive information is achieved by reprocessing the shreds at right angles, to the initial shred, and to a narrower width. Some strip shredders exist where three stage reduction is employed. Disadvantages result because strip shredders are designed to cut the recyclable material into long strips, but are not good at cutting the recyclable material to a desired length.
Single rotor shredders are equipped with square insert cutters that are typically on the order of 32-40 mm square. In operation, the recyclable material is pushed against a rotor so that a gouging action tears out chunks from the recyclable material and insert cutters cut against a fixed knife. A screen may be mounted below a single rotor shredder. When a screen is normally mounted below the single rotor shredder, the holes in the screen retain the recyclable material in the machine until the recyclable material is small enough to fit through the screen holes. As a result, the recyclable material recirculates through the single rotor shredder until it fits through the holes. Disadvantages result because of the increased amount of time that the recyclable material must recirculate to fit through the small holes necessary to shred the recyclable material to a high security shred size. Additional disadvantages result because a high security shred size requirement could have a significantly negative impact on throughput capacity when the screen hole size is significantly smaller than the initial first cut shred size. Yet additional disadvantages result because recirculation of the recyclable material leads to generating dust and heat. Moreover, as recyclable materials frequently contain metal contaminants, recirculation may cause fires and dust explosions in the presence of contaminants that generate sparks. More ignition sources are created as the size of the screen holes decreases. Yet another disadvantage results because obtaining the smaller shred size for highly sensitive information requires the screen to be changed to a screen having smaller holes. Changing the screen is time consuming and difficult, if not impossible, in some designs because it could require physical access through a shredded material storage area to access the shredder. When a screen is not mounted below the single rotor shredder, disadvantages result because single rotor shredders do not tightly control the rotor to fixed knife clearance, thereby allowing the recyclable material to pass through the single rotor shredder without being shredded.
Hammermills are single rotor shredders with hammers mounted on the periphery of the rotor that turn at a high speed (on the order of 900-3600 RPM). When the hammers impact relatively stationary recyclable material, chunks of the recyclable material are torn away. A sizing screen is placed at the bottom of the hammermill and the recyclable material cannot pass through the screen until the recyclable material is smaller than the holes in the screen. Disadvantages result because the recyclable material must be recirculated to reach a size where the recyclable material can pass through the holes in the screen, thereby increasing shred time and generating dust and heat. Additional disadvantages result because reduced screen hole size reduces throughput capacity. Moreover, the recirculation may cause fires and dust explosions. Further disadvantages result when the recyclable material is metal because the hammers may cause the recyclable material to ball up. Once balled up, the recyclable material may never reach a size that is small enough to pass through the holes in the screen. Yet another disadvantage results when the hammers are dull as the dullness causes inefficient shredding, leads to longer shred time, lowers throughput and creates more dust. Additional disadvantages result because hammermills must be meter fed because they are susceptible to rotor jamming if overloaded.
Granulators are high speed single shaft knife cutters that consist of a high speed rotor (450-3600 rpm) with straight rotor blades that cut against fixed straight blade knives. The rotor is typically equipped with 3-5 fixed blades that cut against 1-3 fixed blades. A screen retains the recyclable material until the recyclable material reaches a size where it can pass through the screen holes. Granulators depend on very sharp knives for efficient production. Disadvantages result from the need to have highly trained personnel to maintain the tight knife-to-knife clearances (on the order of 0.004-0.006 inches that are required for efficient shredding. Recyclable materials are difficult for granulators since removal of metal contaminants which are inevitably contained in recyclable materials would be necessary, otherwise the keen sharp-edged blades in a granulator could quickly degrade. Additional disadvantages result as granulators must be meter fed because they are susceptible to rotor jamming if overloaded.
A need exists for improved technology, including technology that may address one or more of the above described disadvantages. For example, a need exists to give a user the option to shred recyclable material to a standard shred size or a smaller shred size required for highly sensitive information via a single pass through the system, where such a single pass produces less dust and less possible ignition sources, and for the user to pay a minimum price with minimum wear and tear of the equipment used to shred the recyclable material.